X-ray or gamma ray systems or devices – Specific application – Computerized tomography
Reexamination Certificate
2000-02-07
2001-10-02
Porta, David P. (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Computerized tomography
C250S367000, C250S368000
Reexamination Certificate
active
06298113
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to an x-ray damage shield and a method of manufacturing the shield. More particularly, it relates to a self aligning x-ray damage shield for protecting an inter-scintillator reflector and a method of manufacturing such a shield.
Solid state detectors for computed tomography (CT) imaging use scintillators to convert x-rays into scintillation light which itself is converted to an electrical signal with a photodiode. Detector arrays are typically comprised of scintillator pixels separated by a reflecting material used to pipe the scintillation light towards the diode. Scintillator thicknesses and pixel widths required by such detectors result in aspect ratios (the ratio of the height to width of a pixel) such that on average, the scintillation light reflects off the reflecting material several times before exiting to the diode. For this reason, the materials useful as a reflector are limited to materials that are highly reflecting at the scintillation light wavelengths emitted by the scintillator.
Appropriate reflector materials include high refractive index solid materials such as TiO
2
formed in a castable low index medium such as an epoxy. One drawback of such a system is the darkening of the epoxy matrix when it is struck by a dose of x-rays commonly used in CT imaging. A typical dose over the life of the detector is 1 Mrad. This darkening results in lower reflectivity and less efficient collection of the scintillation light, and thus a lowering of the sensitivity of the x-ray detector.
Furthermore, the darkening is often not uniform over the entrance face of the detector. This lack of uniformity in darkening can result in image degradation if the detector is not properly calibrated. In addition to the reflector material itself, the diode below the reflector is also sensitive to radiation and must be protected from the x-ray beam.
Current CT detectors use a collimator assembly to protect the reflector epoxy material from damage by x-rays. This assembly consists of tall tungsten plates aligned perpendicular to the plane of the x-ray fan beam. This assembly is primarily used to minimize scattered x-rays from reaching the scintillator, but is also used to protect the reflector material between pixels from the x-rays. For multi-slice CT, where the detector is segmented in the direction parallel to the fan beam, wires are used to protect the reflector and diodes. These wires are strung between the deep plates in grooves machined in the plates.
The manufacturing of such a two dimensional collimator with plates and wires is complex. The separate construction of the collimator with protective wires and the scintillator/reflector body requires accurate alignment of these devices during construction of the complete detector. This alignment cannot be done optically since the reflector material between the scintillator pixels (“interscintillator reflector”) is obscured by reflector material covering the top of the pixels (“surface reflector”). Therefore, either x-ray alignment or rigorous dimensional tolerances must be used to ensure that the reflector material is aligned with the protective wires.
BRIEF SUMMARY OF THE INVENTION
In view of the foregoing, it would be desirable to provide a scintillator pack including a scintillator pixel array, inter-scintillator reflector, and x-ray absorbing layer that avoids or reduces the above mentioned problems.
In accordance with one aspect of the present invention, there is provided a scintillator pack. The scintillator pack includes an array of scintillator pixels, a scintillation light reflecting layer for reflecting scintillation light from the scintillator pixels, where the scintillation light reflecting layer is formed in inter-scintillator regions between the scintillator pixels, and an x-ray absorbing layer comprising a high density x-ray absorbing material formed selectively in first regions over the inter-scintillator regions. Preferably the high density material is formed in a self-aligned manner. The scintillation light reflection layer may cover a top surface of the scintillator pixels.
In accordance with another aspect of the present invention there is provided a method of forming a scintillator. According to this aspect of the invention the method comprises forming a scintillation light reflecting layer in inter-scintillator regions between scintillator pixels of an array of scintillator pixels, and selectively forming an x-ray absorbing layer over the inter-scintillator regions.
According to this aspect of the invention the method may further comprise forming an x-ray absorbing precursor layer over the array of scintillator pixels and inter-scintillator regions, selectively exposing the x-ray absorbing precursor layer to radiation thereby forming first precursor regions selectively over and self aligned to the inter-scintillator regions, and second precursor regions between the first precursor regions, and removing the second precursor regions.
According to this aspect of the invention the method may alternatively further comprise forming a photoresist layer over the array of scintillator pixels and inter-scintillator regions, selectively exposing the photoresist layer to radiation thereby forming first resist regions selectively over the inter-scintillator regions, and second resist regions between the first resist regions, removing the first resist regions formed selectively over the inter-scintillator regions and leaving the second resist regions, forming an x-ray absorbing material over the second resist regions and the inter-scintillator regions, and removing the second resist regions to selectively form the x-ray absorbing layer over the inter-scintillator regions.
According to this aspect of the invention the method may alternatively further comprise forming a photoresist layer over the array of scintillator pixels and inter-scintillator regions, selectively exposing the photoresist layer to radiation thereby forming first resist regions selectively over the inter-scintillator regions, and second resist regions between the first resist regions, selectively exposing the photoresist layer to radiation thereby forming first resist regions selectively over the inter-scintillator regions, and second resist regions between the first resist regions, removing the first resist regions formed selectively over the inter-scintillator regions and leaving the second resist regions, forming a first layer of x-ray absorbing material over the second resist regions and the inter-scintillator regions by one of plating, chemical vapor deposition, sputtering, and evaporation, removing the second resist regions, and optionally forming a second layer of x-ray absorbing material of x-ray absorbing material on the remaining first layer of x-ray absorbing material by one of plating and solder to thereby selectively form the x-ray absorbing layer over the inter-scintillator regions.
In accordance with another aspect of the present invention, there is provided a scintillator pack comprising an array of scintillator pixels, a scintillation light reflecting layer for reflecting scintillation light from the scintillator pixels, where the scintillation light reflecting layer is formed in inter-scintillator regions between the scintillator pixels, and an alignment layer formed selectively in a self aligned manner in first regions over the inter-scintillator regions. The scintillator pack may include an x-ray protection shield formed over and aligned to the alignment layer.
In accordance with another aspect of the present invention, there is provided a method of forming a scintillator pack comprising forming a scintillation light reflecting layer in inter-scintillator regions between scintillator pixels of an array of scintillator pixels, and selectively forming an alignment layer over the inter-scintillator regions. According to this aspect of the invention the method may further comprise forming an x-ray shield over and aligned to the alignment layer. According to this aspect of the invention, t
Bortscheller Jacob Charles
Duclos Steven Jude
Morse Christopher Jay
Taylor George William
General Electric Company
Johnson Noreen C.
Porta David P.
Stoner Douglas E.
Yun Jurie
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